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. Author manuscript; available in PMC: 2014 Nov 1.
Published in final edited form as: Paediatr Perinat Epidemiol. 2013 Nov;27(6):10.1111/ppe.12077. doi: 10.1111/ppe.12077

TABLE 5.

Comparison of Unadjusted and Adjusted Odds Ratios of Autism Spectrum Disorders Among Singleton Pregnancies in the Autism Birth Cohort Study with the Same Unadjusted and Adjusted Odds Ratios in the Medical Birth Registry of Norway

Exposuresa Medical Birth Registry of Norway
Autism Birth Cohort Study
Ratio of Unadjusted OR [95% CI]c Ratio of Adjusted OR [95% CI]c
Unadjusted OR [95% CI]b Adjusted OR [95% CI]b Unadjusted OR [95% CI]b Adjusted OR [95% CI]b
Primipara pregnancy 1.27 [1.16, 1.39] 1.23 [1.11, 1.35] 1.40 [1.08, 1.82] 1.41 [1.06, 1.89] 1.10 [0.86, 1.42] 1.15 [0.88, 1.51]
Prenatal folic acid use 0.66 [0.60, 0.73] 0.84 [0.76, 0.93] 0.70 [0.54, 0.90] 0.83 [0.63, 1.10] 1.06 [0.82, 1.34] 1.00 [0.77, 1.28]
Prenatal smoking 1.31 [1.17, 1.46] 1.17 [1.04, 1.33] 1.37 [0.97, 1.95] 1.20 [0.84, 1.72] 1.05 [0.74, 1.41] 1.02 [0.71, 1.38]
Preterm birth (<37 weeks) 1.57 [1.34, 1.85] 1.49 [1.27, 1.76] 1.82 [1.14, 2.91] 1.67 [1.04, 2.68] 1.16 [0.68, 1.71] 1.11 [0.66, 1.66]
Low birthweight (<2,500 g) 1.85 [1.53, 2.22] 1.70 [1.41, 2.05] 2.08 [1.19, 3.64] 1.84 [1.05, 3.24] 1.12 [0.58, 1.77] 1.08 [0.56, 1.73]
Male sex 4.63 [4.12, 5.21] 4.72 [3.33, 6.69] 1.02 [0.75, 1.48]
Cesarean section historyd 0.95 [0.79, 1.13] 0.98 [0.82, 1.17] 0.99 [0.57, 1.70] 1.00 [0.58, 1.73] 1.04 [0.54, 1.67] 1.02 [0.53, 1.64]

Abbreviations: ASD, autism spectrum disorders; OR, odds ratio; CI, confidence interval.

a

Reference categories for odds ratios were multipara pregnancy, no prenatal folic acid use, no prenatal smoking, term birth (≥37 weeks), normal birthweight (≥2,500 g), female sex, and no cesarean section history.

b

The odds ratios were estimated using logistic regression models and adjusted for the covariates as described in the Methods section. Missing exposure and covariate data were imputed by using a multiple imputation method.

c

The ratio of the odds ratio in the Autism Birth Cohort study over the odds ratio in the Medical Birth Registry of Norway; 95% confidence interval was corrected for inter-dependency between samples by using a non-parametric bootstrap method.

d

Analyses included only women with one or more previous births (Medical Birth Registry of Norway: 1,060 ASD cases among 290,311 children; Autism Birth Cohort study: 108 ASD cases among 48,883 children).